Hydrogen is widely believed to be a major solution to greenhouse gas mitigation and sustainable development of the world economy. Industry already consumes about 600 billion cubic meters of hydrogen per year in various applications, which corresponds to a worldwide hydrogen market of several hundreds of billions of dollars. In addition to auto-makers that are investing significantly in hydrogen vehicle development, hydrogen demand from other industries like the chemical, fertilizer and petrochemical industries is rising rapidly. In Alberta, Canada, oil sands development is requiring large quantities of hydrogen to upgrade bitumen to synthetic crude. Dincer I. Technical, environmental and exergetic aspects of hydrogen energy systems. International Journal of Hydrogen Energy 2002; 27(3):265-285 has outlined many of the key technical and environmental concerns of hydrogen production. Unlike SMR (steam-methane reforming) technology (Rosen M A. Thermodynamic investigation of hydrogen production by steam-methane reforming. International Journal of Hydrogen Energy 1992; 16(3): 207-217), nuclear-based hydrogen production does not emit greenhouse gases. The rise in oil and natural gas prices and the need to sequester CO2 has tilted the economic balance away from the traditional SMR technology. A comprehensive overview of various hydrogen production schemes has been presented by Yildiz and Kazimi (Yildiz B, Kazimi M S. Efficiency of hydrogen production systems using alternative energy technologies. International Journal of Hydrogen Energy 2006; 31:77-92). Rosen M A, Scott D S. Exergy analysis of hydrogen production from heat and water by electrolysis. International Journal of Hydrogen Energy 1992; 17(3): 199-204 evaluated the thermodynamic efficiency of electrolytic hydrogen production from nuclear energy and other sources.
Electrolysis is a proven, commercial technology that separates water into hydrogen and oxygen using electricity. Net electrolysis efficiencies (including the heat-to-electricity efficiency for thermal power plants) are typically about 24%. In contrast, thermochemical cycles to produce hydrogen using nuclear heat can achieve heat-to-hydrogen efficiencies up to 50% or higher. Thermochemical “water splitting” requires an intermediate heat exchanger between the nuclear reactor and hydrogen plant, which transfers heat from the reactor coolant to the thermochemical cycle (Forsberg C W. Hydrogen, nuclear energy and advanced high-temperature reactor. International Journal of Hydrogen Energy 2003; 28:1073-1081). An intermediate loop prevents exposure to radiation from the reactor coolant in the hydrogen plant, as well as corrosive fluids in the thermochemical cycle entering the nuclear plant.
A technical challenge of thermochemical hydrogen production is to provide high temperatures typically above 800° C., which are currently unavailable from nuclear reactors. A recent study (Granovskii M, Dincer I, Rosen M, Pioro I. 2008. Thermodynamic analysis of the use of a chemical heat pump to link a supercritical water-cooled nuclear reactor and a thermochemical water-splitting cycle for hydrogen production, JSME Journal of Power and Energy Systems, 2008; 2: 756-767) has linked the concepts of chemical heat pumps to nuclear-based hydrogen production for this purpose of raising the temperatures. However, this invention differs with the recent study in several regards. It shows specifically how and where heat pumps can be integrated into the thermochemical cycle. The past study involves a different system with methane, much higher temperatures (600° C., not waste heat at 80° C.) relevant to different thermochemical cycles and next-generation nuclear reactors (excluding upgrades of waste heat from near-term nuclear reactors), inclusion of vapour compression as well as other chemical heat pumps, sequential stages of heat pumps and other differences.